1. Field of the Invention
The present invention relates to a substrate treatment method and a substrate treatment apparatus for treating a substrate (particularly, treating a substrate with a treatment fluid such as a treatment liquid) while rotating the substrate. Examples of the substrate to be treated include various types of substrates such as semiconductor wafers, glass substrates for liquid crystal display devices, glass substrates for plasma display panels, substrates for optical disks, substrates for magnetic disks, substrates for magneto-optical disks and substrates for photo-masks.
2. Description of Related Arts
In the production of a semiconductor device, an etching process is often performed, after a thin metal film such as a thin copper film is formed on the entire front surface and peripheral surface (and the entire rear surface in some case) of a semiconductor substrate (hereinafter referred to simply as “wafer”), for etching away unnecessary portions of the thin metal film. For example, a thin copper film for wiring is merely required to be provided in a device formation region on the front surface of the wafer, so that portions of the copper thin film present on a peripheral edge portion of the front surface of the wafer (having a width of about 5 mm as measured from the peripheral edge of the wafer) and the peripheral surface and rear surface of the wafer are unnecessary. In addition, metallic or ionic copper deposited on the peripheral edge portion, the rear surface and the peripheral surface is likely to contaminate a hand of a substrate transport robot provided in a substrate treatment apparatus, and the contamination may be transferred to another substrate held by the hand.
Similarly, a non-metallic film (such as an oxide film or a nitride film) formed on the peripheral surface of the substrate is thinly etched for removal of metal contaminants (including metal ions) from the surface.
A typical substrate periphery treatment apparatus for selectively etching away portions of a thin film from the peripheral edge portion and peripheral surface of a wafer includes, for example, a spin chuck for rotating the wafer while horizontally holding the wafer, a shield plate provided above the spin chuck for limiting a space above the wafer, and an etching liquid supply nozzle for supplying an etching liquid to a lower surface of the wafer. The etching liquid supplied to the lower surface of the wafer flows over the lower surface of the wafer radially outwardly from a rotation center by a centrifugal force, and further flows over the peripheral surface of the wafer onto an upper surface of the wafer, whereby unnecessary substances are etched away from the peripheral edge portion of the upper surface of the wafer. At this time, the shield plate is located adjacent the upper surface of the wafer, and an inert gas such as nitrogen gas is supplied to the space between the shield plate and the wafer.
The amount of the etching liquid flowing onto the upper surface can be controlled by properly adjusting the flow rate of the inert gas and the rotation speed of the spin chuck, so that a peripheral edge portion of the upper surface of the wafer having a predetermined width (e.g., 1 to 7 mm) can selectively be subjected to the etching process (so-called bevel etching process).
The spin chuck includes a vertical rotary shaft, a spin base fixed to an upper end of the rotary shaft, and three chuck pins provided upright on a peripheral edge portion of the spin base. A torque is applied to the rotary shaft with the peripheral surface of the wafer clamped by the chuck pins, whereby the wafer is rotated together with the spin base.
During the rotation of the wafer held by the spin chuck, the unnecessary substances are etched away from the peripheral edge portion of the upper surface of the wafer by supplying the etching liquid to the lower surface of the wafer. After the upper and lower surfaces of the wafer are rinsed with deionized water, the spin chuck is rotated at a high speed to spin off water droplets from the upper and lower surfaces of the wafer for drying the wafer.
With this arrangement, however, the wafer is constantly clamped by the chuck pins, so that portions of the peripheral surface of the wafer kept in abutment against the chuck pins are liable to suffer from a treatment failure such as insufficient etching, insufficient rinsing or insufficient drying.
One approach to this problem is to once stop the rotation of the spin chuck during the treatment, then change wafer clamping positions and resume the rotation of the spin chuck. However, this approach is disadvantageous because the treatment time per wafer is prolonged and the productivity is drastically reduced.
Another conventional approach is disclosed in Japanese Unexamined Patent Publication No. 2001-118824, in which the wafer clamping positions are changed without stopping the rotation of the spin chuck by completely or slightly releasing the wafer from the chuck pins to relatively rotate (or slide) the wafer with respect to the spin chuck and then clamping the wafer again by the chuck pins during the rotation of the spin chuck.
In this conventional approach, however, the wafer is kept in sliding contact with the chuck pins of the spin chuck, because the wafer clamping positions are changed by sliding the wafer on the spin chuck. This results in generation of particles.
In the conventional approach described above, an air cylinder and a link mechanism are incorporated in the spin base for driving the chuck pins, and compressed air is supplied for driving the spin base. This complicates the construction of the apparatus, making the wafer clamping/unclamping motions of the chuck pins unstable.
With the aforesaid arrangement, the chuck pins are kept in sliding contact with the peripheral surface of the wafer during the relative rotation of the wafer with respect to the spin chuck, so that the chuck pins are abraded.
Further, the degree of the relative rotation of the wafer with respect to the spin chuck cannot accurately be controlled, so that the rotational position of the wafer cannot be controlled.
When the wafer is unclamped from the chuck pins during the treatment, a minute spacing between the wafer and the shield plate cannot be kept constant. This makes it impossible to accurately control the amount of the etching liquid flowing onto the front surface from the rear surface of the wafer.